# Re: \[PATCH 22/28\] sgiseeq: convert from dma\_cache\_sync to dma\_sync\_single\_for\_device

- From: Christoph Hellwig \<hch@lst.de\>
- Date: 2020-09-03 08:43:11 
- List: linux-arm-kernel
- Page: https://ratatoskr.run/linux-arm-kernel/2020/09/6092678
- Thread: https://ratatoskr.run/alsa-devel/2020/08/6073543/t/2.md

```text
On Tue, Sep 01, 2020 at 07:38:10PM +0200, Thomas Bogendoerfer wrote:
> this is the problem:
> 
>        /* Always check for received packets. */
>         sgiseeq_rx(dev, sp, hregs, sregs);
> 
> so the driver will look at the rx descriptor on every interrupt, so
> we cache the rx descriptor on the first interrupt and if there was
> $no rx packet, we will only see it, if cache line gets flushed for
> some other reason.

That means a transfer back to device ownership is missing after a
(negative) check.

> kick_tx() does a busy loop checking tx descriptors,
> with just sync_desc_cpu...
> 
> Thomas.
> 
> -- 
> Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
> good idea.                                                [ RFC1925, 2.3 ]
---end quoted text---

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